His Greatest Mistake
by Scribe Teradia
Summary: He would never forgive himself for changing his mind...


**Disclaimer:** I don't own J.K. Rowling's universe, I just like to play with her characters on occasion.

**Author's Note:** This was inspired by the fabulous Christev! Her dark!fic at the On-line Wizarding Library entitled 'Good Things Come to Those Who Wait' contained the line: _Seeing Sirius' face when he realized he'd been had was worth all those taunts and teases._ It hatched a plot-bunny in my brain that wouldn't go away, so here's Sirius' take on Peter's betrayal.

**His Greatest Mistake**  
by Scribe Teradia

He would never forgive himself for changing his mind, even though he'd thought, at the time, that it was the right thing to do. The _safe_ thing to do, when Dumbledore said that the Potters needed to go into hiding. He was James' first choice to be their Secret-Keeper, but then he'd been James' first choice in just about everything since that first fateful meeting on the Hogwarts Express (the notable exception being in the bedroom, where James' first choice had always been Lily Evans, a choice that Sirius would not ever hold against him), so it came as no surprise that he'd be chosen for this, too.

It was an honor almost as great as the day they'd asked him to be little Harry's godfather, and he'd been only too happy to accept, at first. As the minutes ticked by and the darkness spread like a shroud over the land, however, he started having second thoughts. The hours poured out one on top of the other until it had been nearly three days, and by then he could feel the familiar sting of the sharp talons of madness clawing at his skull like an enraged hippogriff. He hated this part of himself, abhored the darkness more than anything else, but at the same time he was deeply terrified. Not for himself, never for himself, but for James and Lily and little Harry, who were so willing to place their trust in him, their lives in his hands. He was terrified because he didn't really know what he was capable of when the madness took hold (he told himself he wouldn't _really_ have tried to kill Snape if he'd been in his right mind, even if he _did_ loathe the Dark Arts-loving little half-blood bastard), and he couldn't bear to risk the safety of the people he loved most in the world. If the decision were really up to him, he'd carry their secret to his grave and be glad of it, but he had to allow for the possibility that, when darkness met darkness as it inevitably would if he carried through with the plan, the traitorous part of his fractured self would spill the secret freely.

He worried himself over it so much that he finally escaped into dog form out of desperation, and while the simple animal thoughts provided a much-needed respite from the stress, the darkness was still there, hovering on the edges of his awareness, lying in wait for when he reverted to his human form. It was too much for a man or a dog to bear, and finally he told James he'd changed his mind, at the last possible second, though he couldn't bring himself to tell his best friend and brother in all but blood that the reason he'd changed his mind was that he knew he couldn't be trusted. As much as he never backed down from a challenge, as much as he welcomed danger and laughed in the face of it, he refused to gamble with the lives of the only real family he'd ever had; he loved them too much for that.

Then came the great debate over who should receive the honor in his place, a decision they couldn't make lightly. It should have been Remus, he was the natural choice to take Sirius' place, but he'd been so strange and shifty lately that Sirius was almost certain that he was a spy, and as horrible as that was to contemplate, it was worse that he couldn't tell James about it, because James trusted Remus almost as much as he trusted Sirius. Which left only Peter (Peter the pudgy, Peter the pathetic), and the irony of trusting the _rat_ was not lost on either of them, but there simply was no one else. That should have been a warning, that things had deteriorated between the four of them so badly that it was Peter they trusted over Remus, but for all his faults (and they were many) Peter had never proven disloyal to any of them, although that could have simply been due to lack of opportunity.

*** * ***

His first clue that something was wrong wasn't Remus' shout ringing through the warded Floo in the dingy flat he'd holed up in. Nor was it the banging on the door of what he presumed to be the Aurors coming to arrest him. It was something he could never have explained to anyone, a hidden instinct that felt like a bubble of something dark and sinister rising in his chest, expanding and popping just beneath his breastbone, accompanied by a soft, maniacal giggle that reminded him eerily of Bella.

By the time the Aurors had broken through the wards and then broken down the door, Sirius had already slipped out the window. He stunned the man standing guard over his motorbike before taking off into the still-dark sky toward Godric's Hollow, where he discovered the remains of the Potters' house and the half-giant blubbering like a baby, the boy cradled in one massive hand. Pressing his keys into Hagrid's other hand, Sirius danced backward before the man could take a swing at him, and as he dodged around a tree he turned into a dog; he knew he was risking exposure with such a reckless move, but he was past caring because now it was only his life on the line. His, and the rat's.

Rat-scent was everywhere, the whole place reeked of it, and Sirius-as-Padfoot snarled before nosing about to find where the scent was freshest, to find where Peter-the-rat had gone. He was behind, too far behind, but he could catch up, overtake the rat and catch it, sink his teeth into fur and flesh and bone and shake and shake until the rat was still. Everything was so much simpler in this body, in this mind, without the complications of morals or complex thoughts to get in the way, only instinct and simple thoughts of running and tracking and kill-the-rat.

The running and tracking were effortless, they required no real thought, and the feel of the wind ruffling his fur was welcome even if the chill in the air was colder than usual for the first of November. He felt free, unchained, and avoided the human-thoughts that tried to creep in about just how free he really was and why. The rat, he knew, had something to do with it, the rat who had run with him and scampered around his paws had done something to incur human-wrath, and there was to be no more running, no more scampering, no more play because the rat was not the friend he had pretended to be.

It was after sunrise when the trail of rat-scent finally got strong enough to let him know that he was close. He didn't slow his pace, never stopped running, but he lifted his head from the ground, no longer tracking by scent alone but looking for some sign that the rat had been this way. His jaws ached at the thought of rending and tearing, and while he'd never killed anything before, he knew he could do it, knew it would be easy, especially if the rat was still a rat. A snap of teeth, a shake of his head, a clean death that was so much more than the rat deserved.

There! He caught sight of a flash of fur, a whipcrack of the wormy tail, and then the rat was gone, the pathetic human standing in its place. The urge was overwhelming to launch himself at the man, to snap his jaws and tear out that soft, fleshy throat and let the blood spill, but the human-thoughts were crowding him again, pressing and pressing... Sirius returned to himself with a start, his jaws still aching with the desire to tear out Peter's throat. Even with his wand in his hand, magic at his disposal, he was all but shaking with the need to change back to the dog, to rip and tear and rend and claw. Instead, he settled for the human way of settling differences, and bellowed, "COWARD!"

Peter was sniveling and shaking in terror, backing away and looking as though he might piss his trousers at any moment; this was fine with Sirius, he wanted Peter to be scared, wanted him to be fucking _terrified_ before he killed him. He was babbling something about mercy, about old times' sake, and Sirius wanted to hear none of it because he couldn't afford to feel even a spark of pity for this pathetic creature who had gotten his best friend -- no, his _family_ -- killed. It hadn't even registered with him yet that they were on a Muggle street, that the Muggles were listening to his ranting and Peter's pleas, he was too busy trying to decide the best way to kill him.

Then Peter did something completely unexpected: he stopped backing away. He sneered nastily and said, "This was all _your_ fault. Yours and _his_. _You_ turned me into a spy, did you really think I wouldn't listen to see what you really thought of me? I know you think I'm stupid, and so did he. Well, he got what he deserved, and so will you."

It happened so fast that Sirius was never quite sure how he managed to remember as many details as he did. In his memory, time seemed to slow, enough for him to catch a clear glimpse of every Muggle on the street, particularly those nearby. A few businessmen, dressed in suits and carrying briefcases. An elderly couple, walking hand in hand. A pair of girls who looked as though they were barely legal, girls he'd have flirted with had the circumstances allowed for it. And a young woman pushing a pram with a baby inside, an older child trotting along beside her. Peter had his wand in hand, his face contorted with hatred and fury, and he pointed it at his opposite hand, his lips moving soundlessly in an incantation that made Sirius' heart constrict with fear and pain. Then the world exploded, and he saw stars, saw the whipcrack flash of the wormy rat's tail, and finally blacked out.

When he came to, it was to two Aurors standing over him, their arrival recent enough that they hadn't yet taken his wand from him. They were asking questions, but his head was ringing still and he didn't understand them. There was an enormous crater in the middle of the street, and red bits of... something he really didn't want to think too hard about. On the fringes of the crowd, just at the limits of his vision, he spotted a rat with a bloodied paw, and something snapped inside of him. Sirius leaped to his feet, his wand in hand, and was flinging every curse he could think of toward the creature, which in retrospect probably wasn't the smartest way to handle the situation. Indeed, the outburst combined with the twelve dead Muggles (they were fairly sure it was twelve, although they never did find all of the pieces) and Pettigrew's finger explained why he was thrown into Azkaban without a trial. He knew, though, that Peter was alive, and someday... someday he'd get his teeth on that rat.

**The End**


End file.
